AGB碳星中的氟
Fluorine in AGB Carbon Stars Revisited
摘要：
利用分子HF（1-0）R9谱线2.3358 $μ$ m对银河系AGB三颗碳星（TX Psc，AQ Sgr和R Scl）的氟丰度进行了再分析。高分辨率（R $\sim 50000$）和高信噪比光谱获得的CRIRES摄谱仪和VLT望远镜或从NOAO档案（TX Psc）已被使用。我们的丰度分析使用了最新一代的MARCS模型大气冷富碳恒星。利用LTE中的光谱合成，我们得出了这些恒星的氟丰度，相对于Jorissen、Smith和Lambert（1992）以前的唯一估计值，它们平均系统地低了$\sim 0.8$ dex。这种差异的可能原因进行了探讨。我们得出结论，这种差异可能依赖于与C-轴承分子（CN和C $_2$）的混合，这在以前的研究中没有得到适当的考虑。新的F丰度与低质量AGB星的全网络恒星模型的预测更一致。这些模型还再现了采样恒星中的$s$过程元素分布。这一结果，如果证实在一个更大的样本AGB星，可能会减轻目前的困难，以解释最大的[F/O]比发现Jorissen等人。特别是，它可能没有必要寻找替代核链影响生产的F在AGB星。
英文摘要：
A reanalysis of the fluorine abundance in three Galactic AGB carbon stars (TX Psc, AQ Sgr and R Scl) has been performed from the molecular HF (1-0) R9 line at 2.3358 $μ$m. High-resolution (R$\sim 50000$) and high signal to noise spectra obtained with the CRIRES spectrograph and the VLT telescope or from the NOAO archive (for TX Psc) have been used. Our abundance analysis uses the latest generation of MARCS model atmospheres for cool carbon rich stars. Using spectral synthesis in LTE we derive for these stars fluorine abundances that are systematically lower by $\sim 0.8$ dex in average with respect to the sole previous estimates by Jorissen, Smith & Lambert (1992). The possible reasons of this discrepancy are explored. We conclude that the difference may rely on the blending with C-bearing molecules (CN and C$_2$) that were not properly taken into account in the former study. The new F abundances are in better agreement with the prediction of full network stellar models of low mass AGB stars. These models also reproduce the $s$-process elements distribution in the sampled stars. This result, if confirmed in a larger sample of AGB stars, might alleviate the current difficulty to explain the largest [F/O] ratios found by Jorissen et al. In particular, it may not be necessary to search for alternative nuclear chains affecting the production of F in AGB stars.
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